Expanding brake operating mechanism



Filed Sept. 25,` 1947 2 Sheets-Sheet 1 June 26, 1951 l. WALLER 2,558,595

EXPANDING BRAKE OPERATING MECHANISM June 26, 1951 l. WALLER 2,558,595

EXPANDING BRAKE OPERATING MECHANISM Filed sept. 25, 1947 2 sheets-sheet 2 lllll g v :Na/Emol? I I B), IVN' WALL-ER 4 TTHWEYS Patented June 26,1951

UNITED SATES P EXPAN DING BRAKE OPERATING MECHANISM Application September 23, 1947, Serial No. 775,675

This invention relates to brakes `such as are used on vehicles, comprising a brake-drum with a pair of shoes either pivotally mounted or iloating inside the drum, with means for pressing them outwards against the inner surface of the ldrum to exert the braking eiect, and has for its object to provide an improved construction which is simple and more satisfactory in operation.

According to this invention there is provided in a brake having internal expanding shoes, lan expander mechanism comprising two bell-crank levers pivotally located on a carrier-bracket land engaging respectively the free ends or the two brake-shoes each by one arm, and each having its other arm operatively connected to the brakeoperating rod.

According to a feature of this invention the second arm of one of the bell-.crank levers is directly 'coupled to the operating rod, and engages the second .arm of the other lever to rock it in the brake-.applying direction.

Preferably the engaging surfaces of the ytwo said arms of the levers are shaped to give a relative rolling action between them, with the minimum amount of sliding.

According to another feature of the invention, the carrier-bracket is trough-like and of U- section and the bell-crank .levers are accommodated between the limbs of the bracket :and respectively pivotally engaged with opposite Aends of the bracket by ftrunnions on the levers engaging in recesses .in the end surfaces of the limbs of the bracket. The form of these trunnions and recess is such Aas .to provide considerably lower frictional losses than would be possible with conventional pivot pins large enough to -fcarry the operating loads.

One embodiment of this invention will now be described by way of example, reference being :made to the accompanying drawings, in which:

Figure 1 is an elevation of a brake 'mechanism having an expander mechanism according to this invention,

Figure 2 is a section on a .reduced scale on the line 2 2 of Figure 1, and

VFigure 3 is van'exploded view on a reduced :scale of .the bell-crank levers and their carrier-'bracket showing details of construction.

Aillhebrake is of usual construction in so far as it comprises a brake-drum I9, a xed carrier lplate ,I I mounted within the Adrum I9, two brake shoes I2, I3 pivotally mounted on `the Vcarrier plate `II each 'at one end, an expander mechanism to loperate on the free lends fof the shoes I2, |13 to Claims. (C1. `18S-'78) force them outwards into contact with the drum and springs I l for ywithdrawing the shoes from contact with the drum.

The expander mechanism according to this embodiment of the invention comprises a troughshaped carrier-bracket I5 of U-section which is secured to, or alternatively which floats upon, the Xed carrier plate i I adjacent the free ends lof the shoes I2, i3. Within the trough I5 between the two limbs I thereof there are mounted a pair of bell-crank levers Ila, I'ib each having a long arm i3d or ich which extends lengthwise along the bracket and a short arm |951, or I9b, the short arms engaging respectively with the shoes I2, I3. Each bell-crank lever is formed with lateral extensions 2i! of a trunnion-li'ke formation to constitute its pivotal mounting and these trunnions 2B lie in suitably rounded recesses ZI in the end surfaces of the limbs I6 of the carrierbracket i5. As will be seen from the drawing the .lateral extensions 2S are of wedge form having .their narrower ends rounded to provide an arcuate edge of small radius of curvature. The radius of curvature oi the rounded edge is substantially less than that which would be required for a pivot pin to support the operating loads. The form of the trunnions 2D and recesses 2| provide considerably lower rictional losses than lis possible With conventional pivot pins large enough to carry the operating loads, being in the nature of an arcuate knife edge bearing.

After the expander mechanism is assembled the levers I'ia, i'ib are retained in place by the vaction of the pull-o spring Il acting 'between the shoes i2, I3 and by the brake-operating forces, but in order to retain them in position `during assembly or dismantling of the'` brake, small projections or pins 22 are provided `extending outwards, one from each trunnion 26, to be engaged by spring-plates 23 located on the outer side or" the vlimbs iii 'of the bracket I5. These spring plates 23 are secured to the bracket I5 Vand yield suiiiciently at their ends lto permit the insertion of the levers i la, lib into place so that the pins engage in holes in lthe spring-plate r23 and are retained thereby.

The long arms ita, lh which lie lengthwise in the carrier-bracket i5, overlap one vanother and their .abutting surfaces 24s, b are rounded so rthat Ywhen subjected to angular movement, a rolling .action is obtained between them with as little relative sliding movement as possible.

kThe 'brake-operating rod 25 extends through -an opening in the brake cover plate '26 and this vopening fis sealed against the ingress Aof ldirt and 3 the like by a legging 2l, and then extends through the carrier plate Il to engage the free end of the long arm isa of the more remote lever Ila. The two lever arms ltd, ISD are forked at their ends to accommodate the operating rod 25 between them and the lever arm ld carries a pin 28 engaged by an eye in the end of the operatingrod 25 so that a pull on the rod swings leverarm 18a, inwards and in such movement also moves the lever-arm Ib inwards and swings the short arms i911, lsb outwards to press the shoes l2, i3 into contact with the drum itl.

A stop 2B is providedv on the carrier-bracketV I5 to be engaged by a nose 3d on the end of leverarm Ia to limit the outward movement of the lever-arms ISc, i319 under the action ci the pullof I4.

Suicient clearance is provided in the eye on the operating rod 25 and between the forked ends of lever-arm Ia, lSb so that angular displacement of the rod is possible.

The brake-shoes I2, I3 are of the ordinary T section with the friction lining on the outer side, and the stem of the T directed inwards, and each of the operating levers Ila, i'lb is provided on its short arm iSd, i813 with a slot 3i to engage the end of the stern of the The expander mechanism is secured, as mentioned above, to the carrier-plate I I so that the equivalent of a iixed cam is obtained, which gives equal shoe-travel and equal lining-wear, together with a straight line relationship of brake-factor against lining-iriction-coeicient. in order to provide the desired braking eect, a serve motor may be used.

Alternatively the expander mechanism can be allowed to float on the carrier-plate II, in which case a differential effect arises as between a leading and a trailing shoe. This is advantageous in some circumstances in that a greater braking effect can be obtained owing to the self -applying action of the leading shoe.

In either case an adjuster is required to take care of lining wear, and this can conveniently be of the known type which expands the shoeo abutment points.

The general advantages of this invention are v internal expanding brake shoes within the drum,

a carrier plate for supporting the brake shoes, and pull-off spring means to urge the brake shoes from engagement with the brake drum; an expander mechanism comprising a bracket comprising a base portion adapted to be supported from the carrier plate and a pair of spaced apart limbs upstanding from said base portion and forming therebetween a channel extending substantially from the free end of one brake shoe to the free end of the other brake shoe, the edges of the limbs adjacent each brake shoe being formed with aligned part-circular recesses of small radius of curvature, a pair of bell-crank levers, one for each brake shoe, each bell-crank lever having a short arm, a long arm and a pair of laterally extending trunnion elements, each of such dimensions as to withstand the operating loads and each having asmall radius of curvature bearing surface, each bell-crank lever being disposed with its short arm engaged with its assimplicity of construction, ability to operate satsociated brake shoe, with the bearing surfaces of its trunnion elements engaged in a pair of the aligned part-circular recesses, and with its long arm extending within the channel from one end thereof towards the other end, the inner ends of said bell crank levers being overlapped and in contact, the contacting surfaces being rounded to have substantially rolling contact upon one another incident to the rocking movements of said levers; and an operating member adapted to engage the inner end portion oi the long arm of one of the bell crank levers to rock it and throughv the rounded surfaces rock the other bell crank lever by applying a load to said one bell crank lever in a direction such that the loads on the bell crank levers retain said bearing surfaces oi the laterally extending trunnion elements in engagement with the part-circular recesses.

2. In a brake of the class comprising a brake drum, a pair oi internally-arranged brake shoes Vto co-operate with the brake drum, a carrier plate for supporting the brake shoes, pull-off spring means to urge the brake shoes out from engagement with the brake drum, and an expander mechanism for moving the bra-ke shoes into engagement with the brake drum; a construction of expander mechanism comprising a pair of bell-crank levers, one for each brake shoe; each bell-crank lever having a long arm, a short arm, and a pair of laterally extending parts at the junction of the long and short arms; each laterally extending part forming a trunnion for the bell-crank lever, having such dimensions as to withstand the operating loads and having an arcuate edge oi lsmall radius ci curvature; a channel-section bracket having a pair of limbs upstanding from a base portion and adapted to be supported by the carrier plate with its channel extending from adjacent the end of one brake shoe to adjacent the end of the other brake shoe, the limbs being formed in each of their end edges with small radius part-circular recesses, the recesses in the adjacent ends of the limbs being aligned; the bell-crank levers being disposed in the channel-section bracket with their short arms engaged with the respective brake shoes, with their long arms extending from one end of the channel towards the other end with the arcuate edges of their laterally extending parts engaged with a pair of said aligned recesses; said long arms overlapping and being engaged through rounded surfaces to provide substantially rolling contact therebetween; and an operating member connected with one beilcrank lever to rock it and thereby through said rounded surfaces to rock the other bell-crank lever, by applying a load to said one bell-crank lever in a direction such that the loads on the bell-crank levers retain said arcuate edges in the recesses.

3. An expander mechanism as claimed in claim 2, wherein said laterally extending parts are each of wedge-form having their narrower end shaped to provide the arcuate edges of smallradius of curvature.

4. For use in expanding spring-retracted brake shoes against a brake drum, an expander mechanism comprising a pair oi spaced walls lying in planes substantially normal to the plane cf movement of the brake shoes and cross-wise between the free ends of the brake shoes with end edges of said walls adjacent the ends of the brake shoes having rounded bearing recesses open at their outer sides, bell-crank levers having long and short armsdisposed between said 5 .L walls and between the free ends of the brake shoes, with the short arms engaging with said brake shoes, trunnions projecting laterally from said bell crank levers in opposite directions and fitted to rock in said recesses, said trunnions having rounded inner portions conforming generally to the curvature of' said recesses to enable the levers to rock on said trunnions in said recesses, said trunnions v,being rounded only at their inner end portionsiand having massive outer non-circular portions to reinforce and strengthen the innerrounded bearing portions, the long arms of said levers lying longitudinally of one another with the inner end portions overlapped, said levers havirig mutually rounded bearing contacting surfacesat their overlapped portions, and an operating member connected with one inner end portion of one lever for moving the same toward `the overlapped portion of the other lever incident to expanding the brake shoes to cause theoverlapped rounded surfaces to roll upon one another and the rounded inner trunnion. surfaces to rock in said recesses and to cause the rounded inner trunnion surfaces to seek the recesses incident to the brake loads transmitted by said operating member to said levers.

6 5. An yexpander mechanism as claimed in claim 4 further comprising pins extending laterally beyond said trunnions and detents on the walls engaged by said pins to further hold the inner rounded surfaces of the trunnions in said recesses.

IVAN WALLER.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,631,448 Alden et al. June '7, 1927 2,012,025` Sawtelle Aug. 20, 1935 2,020,578 Sawtelle Nov. 12, 1935 2,037,494 Boughton et a1 Apr. 14, 1936 2,069,344 White Feb. 2, 1937 2,104,735" Carroll et a1. Jan. 11, 1938 2,252,860 Porsche Aug. 19, 1941 j' FOREIGN PATENTS Number Country Date 302,186 Italy Oct. 21, 1932 436,902 Great Britain Oct. 21, 1935 

